Mobile terminal device and method for radiating heat therefrom

ABSTRACT

In a mobile terminal device, at least one heat conduction layer formed of a member, such as copper, aluminum or carbon, being excellent in heat conductivity is provided inside a circuit board on which electronic components are mounted. The heat generated in the electronic components is promptly dispersed in the direction of the face of the circuit board by the heat conduction layer, and transferred from the whole face of the circuit board to the operation member, such as keys, and the housing, and then radiated to the outside. With this structure, the local temperature rise at the operation member and the housing can be suppressed, and the temperature on the surface of the mobile terminal device can be made uniform, without significantly increasing the cost and the thickness of the mobile terminal device. In addition, high-performance electronic components can be used by adopting this structure. Furthermore, the rigidity of the circuit board can be raised, and the reliability of the mobile terminal device can be improved.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to a mobile terminal device and a methodfor radiating heat therefrom, more particularly, to a structure of acircuit board in a mobile terminal device, on which heat-generatingcomponents are mounted, and to a method for radiating heat using thecircuit board.

2. Description of the Related Art

Mobile terminal devices as typified by mobile phones are provided withvarious functions, such as a video phone function, a photographingfunction and a TV broadcast receiving function, in addition to a voicecommunications function and a mail sending/receiving function. For thepurpose of realizing these functions, efforts have been made to improvethe processing capacities of mobile terminal devices. As mobile terminaldevices are made high in function and performance, the power consumed inthe electronic components mounted inside the mobile terminal devicesincreases. As a result, the temperature rises in the mobile terminaldevices have lead to problems.

For the purpose of preventing the temperature rises described above,countermeasures are taken in electronic apparatuses, such as personalcomputers. For example, heat-radiating heatsinks made of metal, fans,etc., are installed on the surfaces of electronic components thatgenerate much heat so that heat can be radiated from the inside of thehousing to the outside. In addition, Japanese Published UnexaminedPatent Application No. Hei 11-95871 discloses a heat-radiating structureof an electronic apparatus, wherein heat conduction films are providedon ribs that are used to raise the rigidity of the housing of a mobilepersonal computer, and heat radiation plates bonded to heat generatingcomponents are made so as to contact with the heat conduction films ofthe ribs so that the heat generated from the heat generating componentsis dispersed efficiently.

However, since mobile terminal devices of recent years have beenrequested to be reduced further in size and thickness, it is difficultto provide such heat-radiating structures as used in personal computersbecause of space limitations. Hence, in a mobile terminal device, it isnecessary to transfer the heat generated in electronic components to thehousing and to radiate the heat from the housing to the outside.However, the surface area of the housing of the mobile terminal deviceis small and does not have sufficient heat-radiating efficiency. Hence,if the amount of heat generated in the electronic components is large,the temperature of the housing eventually rises.

In addition, mobile terminal devices are also required to be reduced inthickness, the clearance between the electronic components and thehousing cannot be increased, and the heat generated in the electroniccomponents is transferred immediately to the surface of the housing. Asa result, a problem of local temperature rising at the surface of thehousing result.

In particular, if the temperature of the operation member, such as thekeys that the user operates, and the temperature of the housing in thevicinity thereof are raised, discomfort is given to the user duringoperation. For this reason, it is desired to propose a mobile terminaldevice capable of effectively radiating the heat generated in electroniccomponents.

SUMMARY OF THE INVENTION

The present invention is intended to provide a mobile terminal devicecapable of suppressing local temperature rising due to the heatgenerated in electronic components disposed inside and to provide amethod for radiating the heat from the device.

A mobile terminal device according to the present invention comprises:

a circuit board,

heat-generating components mounted on the circuit board, and

at least one first heat conduction layer provided inside the circuitboard, in which a member having a heat conductivity higher than that ofthe main constituent material of the circuit board is arranged in thedirection of the face of the circuit board, wherein

the heat generated in the heat-generating components is dispersed to thewhole face of the circuit board via the heat conduction layer.

The present invention can have a configuration wherein theheat-generating components are disposed on one face of the circuitboard.

In addition, the present invention can have a configuration furthercomprising a operation member on the face other than the face of thecircuit board on which the heat-generating components are mounted,wherein at least one heat conduction suppressing layer having a heatconductivity lower than that of the main constituent material of thecircuit board is provided inside the circuit board and between the firstheat conduction layer and the operation member.

Furthermore, the present invention can have a configuration wherein aconnection member formed of a heat conduction member having a heatconductivity higher than that of the main constituent material of thecircuit board and making contact with both of the first heat conductionlayer and the heat-generating components is provided between the firstheat conduction layer and the heat-generating components, and the firstheat conduction layer is thermally connected to the heat-generatingcomponents by the connection member.

Furthermore, the present invention can have a configuration wherein theheat-generating component is provided with a heat-radiating terminalthat makes contact with the first heat conduction layer in a state thatthe heat-generating component is mounted, and the heat conduction layeris thermally connected to the heat-generating component by theheat-radiating terminal. The heat-radiating terminal is a terminal notcontributing to the electrical connection of the heat-generatingcomponent and is preferably connected to the housing of theheat-generating component, or a circuit board or a component inside theheat-generating component. The heat-radiating terminal can be formed ofa solder ball constituting BGA (Ball Grid Array).

Furthermore, the present invention can have a configuration wherein thefirst heat conduction layer is formed on the whole face or part of thecircuit board excluding the areas on which connection wires forconnecting the front and back faces of the circuit board are formed asviewed in the normal direction of the circuit board.

Furthermore, the present invention can also have a configuration whereinnon-heat-resistant components are mounted on the circuit board, and thefirst heat conduction layer is formed on the whole face or part of thecircuit board excluding the areas on which the no-heat-resistantcomponents are mounted as viewed in the normal direction of the circuitboard.

Furthermore, the present invention can also have a configuration whereinthe circuit board is fixed by protruding portions provided beforehand onthe housing of the mobile terminal device, and the members of thecircuit board between the first heat conduction layer and the protrudingportions are removed in at least part of the areas corresponding to theprotruding portions, and the heat conduction layer is thermallyconnected to at least part of the protruding portions.

Furthermore, the present invention can also have a configuration whereinanother circuit board is fixed to the circuit board, at least one secondheat conduction layer in which a member having a heat conductivityhigher than that of the main constituent material of the other circuitboard is arranged in the direction of the face of the other circuitboard is provided inside or on the surface of the other circuit board,the first heat conduction layer of the circuit board is thermallyconnected to the second heat conduction layer of the other circuit boardby the connection member, and the heat generated in the heat-generatingcomponents mounted on the circuit board is transferred to the othercircuit board via the connection member.

Furthermore, the present invention can also have a configuration whereinthe circuit board held in a first housing, an other circuit board heldin a second housing and a connection circuit board for connecting thecircuit board to the other circuit board are provided, at least onesecond heat conduction layer in which a member having a heatconductivity higher than that of the main constituent material of theother circuit board is provided in the direction of the face of theother circuit board is arranged inside or on the surface of the othercircuit board, at least one third heat conduction layer in which amember having a heat conductivity higher than that of the mainconstituent material of the connection circuit board is arranged in thedirection of the face of the connection circuit board is provided insideor on the surface of the connection circuit board, the first heatconduction layer of the circuit board is thermally connected to thethird heat conduction layer of the connection circuit board by theconnection member, and the third heat conduction layer of the connectioncircuit board is thermally connected to the second heat conduction layerof the other circuit board by the connection member, and the heatgenerated in the heat-generating components mounted on the circuit boardis transferred to the other circuit board via the connection member andthe connection circuit board.

Furthermore, in the present invention, the mobile terminal device ispreferably a mobile phone, a mobile computer or a mobile game machine.

Furthermore, a heat radiating method according to the present inventionis a heat radiating method for a mobile terminal device equipped with acircuit board on which at least one heat-generating component ismounted, wherein at least one first heat conduction layer in which amember having a heat conductivity higher than that of the mainconstituent material of the circuit board is arranged in the directionof the face of the circuit board is provided inside the circuit board,and the heat generated in the heat-generating component is dispersed inthe direction of the face of the circuit board by the heat conductionlayer.

The present invention further comprising the operation member on theface other than the face of the circuit board on which theheat-generating components are mounted can have a configuration whereinat least one heat conduction suppressing layer having a heatconductivity lower than that of the main constituent material of thecircuit board is arranged inside the circuit board and between the firstheat conduction layer and the operation member, and the transfer of theheat generated in the heat-generating components to the operation memberis suppressed by the heat conduction suppressing layer.

Furthermore, the present invention can also have a configuration whereinthe first heat conduction layer is thermally connected to theheat-generating components by the connection member formed of a memberhaving a heat conductivity higher than that of the main constituentmaterial of the circuit board, and the heat generated in theheat-generating components is transferred to the first heat conductionlayer via the connection member.

Furthermore, the present invention can also have a configuration whereinprotruding portions for fixing the circuit board are provided on thehousing of the mobile terminal device, the members of the circuit boardbetween the first heat conduction layer and the protruding portions areremoved in at least part of the areas corresponding to the protrudingportions so that the first heat conduction layer is thermally connectedto the protruding portions, and the heat generated in theheat-generating components is transferred to the housing via the heatconduction layer and the protruding portions.

Furthermore, the present invention can also have a configuration whereinat least one second heat conduction layer in which a member having aheat conductivity higher than that of the main constituent material ofthe other circuit board is provided in the direction of the face of theother circuit board is arranged inside or on the surface of the othercircuit board fixed to the circuit board, the first heat conductionlayer of the circuit board is thermally connected to the second heatconduction layer of the other circuit board by the connection member,and the heat generated in the heat-generating components mounted on thecircuit board is transferred to the other circuit board via theconnection member.

Furthermore, the present invention comprising the circuit board held inthe first housing, the other circuit board held in the second housingand the connection circuit board for connecting the circuit board to theother circuit board can also have a configuration wherein at least onesecond heat conduction layer in which a member having a heatconductivity higher than that of the main constituent material of theother circuit board is arranged in the direction of the face of theother circuit board is provided inside or on the surface of the othercircuit board, at least one third heat conduction layer in which amember having a heat conductivity higher than that of the mainconstituent material of the connection circuit board is arranged in thedirection of the face of the connection circuit board is provided insideor on the surface of the connection circuit board, the first heatconduction layer of the circuit board is thermally connected to thethird heat conduction layer of the connection circuit board by theconnection member, and the third heat conduction layer of the connectioncircuit board is thermally connected to the second heat conduction layerof the other circuit board by the connection member, and the heatgenerated in the heat-generating components mounted on the circuit boardis transferred to the other circuit board via the connection member andthe connection circuit board.

With the configuration of the present invention described above, theheat generated in the electronic components is dispersed in thedirection of the face of the circuit board by at least one heatconduction layer arranged in the circuit board on which the electroniccomponents are mounted, transferred from the whole face of the circuitboard to the operation member, such as keys, and the whole of thehousing, further transferred to the other circuit board connected to thecircuit board and the components mounted on the other circuit board, andstill further transferred to the other housing accommodating the othercircuit board, and then radiated to the outside. Hence, the temperaturesof the operation member and the housing do not rise locally, and heatradiation can be carried out efficiently. With this simpleheat-radiating structure, discomfort during operation due to localtemperature rises can be relieved without significantly increasing thecost or the like and without increasing the thickness of the mobileterminal device.

The mobile terminal device and the heat-radiating method according tothe present invention have effects described below.

A first effect of the present invention is that the local temperaturerise at the operation member, such as keys, and the housing due to theheat generated in electronic components can be suppressed and that thetemperature of the surface of the mobile terminal device can be madeuniform. The reason is that the heat generated in the electroniccomponents is dispersed in the direction of the face of the circuitboard by at least one first heat conduction layer arranged in thecircuit board on which the electronic components are mounted,transferred from the whole face of the circuit board to the operationmember and the whole of the housing, further transferred to the othercircuit board connected to the circuit board and the components mountedon the other circuit board, and still further transferred to the otherhousing accommodating the other circuit board, and then radiated to theoutside.

In addition, a second effect of the present invention is that the heatgenerated in the electronic components can be radiated effectivelywithout significantly increasing the cost or the like and withoutincreasing the thickness of the mobile terminal device. The reason isthat the heat generated in the electronic components can be dispersed bya simple structure wherein heat conduction members are arranged inlayers inside the circuit board and then radiated by the operationmember and the whole of the housing, without installing heatsinks madeof metal, fans or the like that are large in size.

Furthermore, high-performance electronic components can be used byadopting this kind of heat-radiating structure. Furthermore, therigidity of the circuit board can be raised by providing the heattransfer layer inside the circuit board. As a result, the deformation ofthe circuit board due to external forces encountered during dropping,key operation and the like can be suppressed, and the connectionreliability of the electronic components can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the configuration of a mobile terminal device;

FIG. 2 is a block diagram showing the basic functions of the mobileterminal device;

FIG. 3 is a schematic sectional view showing a structure of the keyoperation section of the mobile terminal device according to the firstembodiment of the present invention;

FIG. 4 is a schematic view showing how heat is transferred in the keyoperation section of the mobile terminal device according to the firstembodiment of the present invention;

FIG. 5 is a sectional view showing another structure of the keyoperation section of the mobile terminal device according to the firstembodiment of the present invention;

FIG. 6 is a sectional view showing still another structure of the keyoperation section of the mobile terminal device according to the firstembodiment of the present invention;

FIGS. 7A, 7B and 7C are schematic perspective views showing thestructures of electronic components to be mounted on the circuit boardof the mobile terminal device according to the first embodiment of thepresent invention;

FIG. 8 is a sectional view showing a structure of the key operationsection of the mobile terminal device according to the first embodimentof the present invention;

FIG. 9 is a sectional view showing a structure of the key operationsection of the mobile terminal device according to the first embodimentof the present invention;

FIG. 10 is a plan view showing a variation of the shape of a heatconduction layer according to the first embodiment of the presentinvention;

FIG. 11 is a plan view showing variation of the shape of the heatconduction layer according to the first embodiment of the presentinvention;

FIG. 12 is a plan view showing variation of the shape of the heatconduction layer according to the first embodiment of the presentinvention;

FIG. 13 is a schematic view showing how heat is transferred in the keyoperation section of a conventional mobile terminal device;

FIG. 14 is a schematic sectional view showing a structure of the circuitboard of a mobile terminal device according to a second embodiment ofthe present invention; and

FIG. 15 is a schematic sectional view showing another structure of thecircuit board of the mobile terminal device according to the secondembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As described with respect to the background art, as mobile terminaldevices are made multifunctional and high in performance, the amount ofheat generated in electronic components increases. However, since mobileterminal devices are also requested to be reduced in size, weight andthickness, the heatsinks made of metal and the fans being used forpersonal computers and other electronic apparatuses cannot be used forthe mobile terminal devices. As a result, the temperature of theoperation member, such as the keys, and the temperature of the housingare raised locally by the heat generated in the electronic components,thereby causing a problem of giving discomfort to the user during keyoperation.

For the purpose of solving this problem, a structure wherein a heatconduction member is arranged inside the housing (for example, JapanesePublished Unexamined Patent Application No. 2002-323936), a structurewherein a metal chassis is provided inside the housing (for example,Japanese Published Unexamined Patent Application No. Hei 2-262724), astructure wherein the housing itself is formed of a member having a highheat conductivity, such as a magnesium alloy (for example, JapanesePublished Unexamined Patent Application No. 2000-253115), etc., havebeen proposed to raise the heat-radiating effect of the housing.

However, since the mobile terminal devices are required to be reduced inthickness, an operation member, such as numeric keys and direction keys,are directly installed, via a key sheet, on a circuit board on whichelectronic components are mounted. As a result, the heat generated inthe electronic components is transferred directly to the operationmember. Hence, even if the heat conductivity of the housing is improved,the temperature rise at the operation member cannot be suppressed, andthe problem of giving discomfort to the user during key operation cannotbe solved.

In the present invention, instead of a structure wherein a heatconduction member is arranged inside the housing and the housing itselfis formed of a member having a high heat conductivity, a heat conductionmember is arranged inside a circuit board itself on whichheat-generating components are mounted, and the heat generated in theelectronic components is dispersed immediately to the whole of thecircuit board. With this kind of structure, the local temperature riseat the operation member and the housing in the vicinity thereof issuppressed even in a structure wherein the operation member is directlyinstalled on the circuit board via a key sheet, whereby the problem ofgiving discomfort to the user during key operation is solved.

Next, embodiments according to the present invention will be describedin detail referring to the accompanying drawings. FIG. 1 is a viewshowing the basic configuration of a mobile terminal device. FIG. 2 is ablock diagram showing the functions of this mobile terminal device. Inaddition, FIG. 3 is a schematic view showing a sectional structure ofthe key operation section thereof, and FIG. 4 is a schematic viewshowing how heat is transferred. Furthermore, FIG. 5, FIG. 6, FIG. 8 andFIG. 9 are views showing variations of the sectional structure of thekey operation section, FIGS. 7A, 7B and 7C are schematic perspectiveviews showing the structures of electronic components to be mounted on acircuit board according to this embodiment, and FIG. 10 to FIG. 12 areviews showing variations of the shape of a heat conduction layer.Moreover, FIG. 13 is a schematic view showing how heat is transferred ina conventional mobile terminal device. Although a mobile phone is takenas an example of mobile terminal devices and is described below, suchmobile terminal devices should only be equipped with at least anoperation member and a display means, and the configuration thereof canbe applied similarly to any mobile devices, for example, mobilecomputers such as PDAs, slim digital cameras and mobile game machines.

As shown in FIG. 1 and FIG. 2, a mobile terminal device 1 (mobile phone)generally comprises a display section 3, formed of a liquid crystaldisplay device, an EL light-emitting device or the like, for displayingstandby screens, various function setting screens, web screens, etc.; akey operation section 2 having multiple keys, such as numeric keys,direction keys and special function keys; a wireless communicationssection 8 and an antenna 9 for carrying out telephone communications,E-mail sending/receiving, web screen receiving, etc.; a speaker 4 and amicrophone 5 for inputting/outputting sound and for outputting ringtone; an internal storage device 6 for storing various setting values;and a control section 7 for controlling these. Furthermore, variouselectronic components for realizing various functions of the mobileterminal device 1 are disposed inside the key operation section 2.

The sectional structure of the key operation section 2 of the mobileterminal device 1 is as shown in FIG. 3, for example. The key operationsection 2 comprises an upper housing 11; a lower housing 12 fitted tothe upper housing 11; a circuit board 13 arranged inside the upperhousing 11 and the lower housing 12 and held by the protruding portions11 a and 12 a of the respective housings; a key sheet 15 provided on aface of the circuit board 13 on the side of the key operation face ofthe key operation section 2; keys 16, such as numeric keys, directionkeys and special function keys, arranged on the key sheet 15; and atleast one electronic component 14 arranged on the other face of thecircuit board 13 on the opposite side of the key operation face of thekey operation section 2. Inside the circuit board 13, at least one heatconduction layer 17 having the shape of a layer is provided wherein amember (hereinafter referred to as a heat conduction member) having aheat conductivity at least higher than that of the main constituentmaterial (a material constituting the substrate excluding wiringmaterials and the like) of the circuit board 13 is arranged in thedirection of the face of the circuit board 13.

The kind and thickness of this heat conduction member are notparticularly limited, but the heat conduction layer may be formed of ametal material, such as copper or aluminum, or may be formed of amaterial having high electrical insulation, such as carbon. Furthermore,the heat conduction member may be formed of thin films of thesematerials, and may also be formed of thin sheets wherein these materialsare dispersed in a resin or the like. The method for producing thecircuit board 13 is not particularly limited, but a method for producinggeneral multi-layer circuit boards may also be used. In addition, forexample, the circuit board 13 can also be produced by using a methodwherein two substrates on which wiring patterns are formed beforehandare made, the heat conduction layer 17 is formed on the surface of oneof the substrates, and the other substrate is bonded to the heatconduction layer 17 using an adhesive or the like. Although the heatconduction layer 17 is formed at a nearly central position in thethickness direction of the circuit board 13 in the figure, the heatconduction layer 17 should only be formed inside the circuit board 13.In other words, the heat conduction layer 17 may be formed at a positionclose to the face on which the electronic components 14 are mounted ormay also be formed at a position close to the other face that is closeto the key operation face of the key operation section 2.

In addition, although two electronic components 14 are mounted on thecircuit board 13 in the figure, the number, size, disposition and thelike of the electronic components 14 are not limited. Among theelectronic components 14, at least one electronic component 14generating heat (a heat-generating component whose temperature is raisedto a temperature at least higher than the ambient temperature whendriven, for example, a power amplifier, a charging IC or the like)should only be included. Furthermore, the configuration of eachelectronic component 14 is not limited. In other words, the electroniccomponent 14 may be a component for realizing its individual function,such as a transistor or a transformer, or may be an assembly comprisingmultiple components for realizing their individual functions, such as anamplifier or a voltage converter. Furthermore, although the electroniccomponents 14 are mounted on only one face of the circuit board 13 inthe figure, in the case that there is space on the other face of thecircuit board 13 (on the side of the key operation face), the electroniccomponents 14 may also be mounted on the side of key operation face.

Next, how the heat generated in the electronic components 14 mounted onthe circuit board 13 is transferred will be described referring to thefigures.

First, in the case of a conventional mobile terminal device wherein noheat conduction layer is formed inside the circuit board 13, when heatis generated in either one of the electronic components 14 mounted onone face of the circuit board 13 as shown in FIG. 13 (a heat-generatingportion 19 is indicated in black in the figure), the generated heat istransferred from the electronic component 14 to the circuit board 13since the generated heat is hard to be transferred to an air layer 18but apt to be transferred in the direction of an object making contactwith the electronic component 14. Hence, the generated heat istransferred from the electronic component 14 to the circuit board 13,thereby being dispersed isotropically inside the circuit board 13. Sincethe thickness of the circuit board 13 is sufficiently smaller than thedimensions in the direction of the face, the heat dispersed into thecircuit board 13 is promptly transferred to the opposite face of thecircuit board 13, and further transferred to the respective keys 16 viathe key sheet 15 installed on the opposite face of the circuit board 13.For this reason, only the keys 16 disposed close to the electroniccomponent 14 generating heat and the upper housing 11 in the vicinitythereof tend to be heated to high temperatures.

The keys 16 are formed separate from the housing (the upper housing 11in this case) so that they can be pressed. In addition, the key sheet 15is disposed separate from the housing so as not to be pressed byanything other than the keys 16. Hence, even if a heat conduction memberor a metal chassis is provided on the inside face of the housing or evenif the housing itself is formed of a heat conduction member, as in theconventional examples, the heat directly transferred to the keys 16cannot be radiated effectively. Therefore, it is impossible to suppressthe local temperature rise at the keys 16 and the housing.

Contrary to this, in the case of the mobile terminal device 1 accordingto this embodiment, as shown in FIG. 4, although the heat generated inthe electronic components 14 mounted on one face of the circuit board 13is similarly transferred to the circuit board 13, since the heatconduction layer 17 being excellent in heat conductivity is arranged inthe shape of a layer in the direction of the face of the circuit board13 inside the circuit board 13, the heat transferred to the circuitboard 13 is promptly dispersed in the direction of the face of thecircuit board 13 via the heat conduction layer 17. Furthermore, the heatdispersed to the whole of the heat conduction layer 17 is transferred tothe whole face on the opposite side of the circuit board 13, and thentransferred to all the keys 16 via the key sheet 15. Moreover, the heatis also transferred to the upper housing 11 and the lower housing 12 viathe protruding portions 11 a and 12 a that are used to hold and fix thecircuit board 13. For this reason, even if the electronic components 14generate heat, it is possible to prevent the problem of raising thetemperatures of only the keys 16 and the upper housing 11 in thevicinity of the electronic components 14.

Although only the heat conduction layer 17 is provided inside thecircuit board 13 in FIG. 3 and FIG. 4, it is also possible to provide astructure wherein the heat conducted to the heat conduction layer 17 ishard to be transferred to the key sheet 15 and the keys 16. For example,as shown in FIG. 5, a heat conduction suppressing layer 22 having agiven thickness is provided closer to the side of the key operation facethan the heat conduction layer 17 inside the circuit board 13, and theheat conducted to the heat conduction layer 17 is radiated to sectionsother than the key sheet 15 and the keys 16 (for example, the upperhousing 11 and the lower housing 12 via the protruding portions 11 a and12 a) by the heat conduction suppressing layer 22. With thisconfiguration, the temperature rise at the keys 16 can be suppressed.The heat conduction suppressing layer 22 may be formed of, for example,a member at least having a heat conductivity smaller than that of themain constituent material of the circuit board 13, or areas having asmall heat conductivity may be formed in the circuit board 13 byproviding minute pores in the circuit board 13 so as to function as theheat conduction suppressing layer 22.

Furthermore, although only the heat conduction layer 17 having the shapeof a layer is provided inside the circuit board 13 in FIG. 3 and FIG. 4,it is also possible to provide a structure wherein the heat generated inthe electronic components 14 can be promptly transferred to the heatconduction layer 17. For example, as shown in FIG. 6, at least oneconnection portion 17 a connected to the heat conduction layer 17 isformed at the portion of the circuit board 13 on which the electroniccomponent 14 generating heat is mounted, and the electronic component 14is mounted so as to make contact with the connection portion 17 a (forexample, the connection portion 17 a is formed so as to protrude fromthe circuit board 13, and the protruding portion is crushed when theelectronic component 14 is mounted). With this configuration, the heatconduction layer 17 is thermally connected to the bottom faces of theelectronic component 14, and the heat generated in the electroniccomponent 14 can be transferred promptly to the heat conduction layer17. The method for forming the connection portion 17 a is notparticularly limited. However, for example, it may be possible that atleast one hole reaching the heat conduction layer 17 from the componentmounting face is formed at the portion of the circuit board 13 on whichthe electronic component 14 is mounted and that a heat conduction member(the member may be the same member as that of the heat conduction layer17 or may be a member different therefrom) is embedded inside the hole.Furthermore, it may also be possible that at least one through holepassing through the circuit board 13 from the side of the key operationface is formed and that the abovementioned heat conduction member isembedded inside the through hole.

In addition, in the case that the connection portion 17 a describedabove is formed, it may also be possible that a member having a highheat conductivity, such as a metal plate 23, is provided beforehand onthe component mounting face of the circuit board on which the electroniccomponent 14 is mounted as shown in FIG. 7A and that this metal plate 23is made so as to contact with the connection portion 17 a. Furthermore,in the case that the electronic component 14 is connected to the circuitboard 13 by BGA (Ball Grid Array), it may also be possible that at leastone connection solder ball 24 a not contributing to the electricalconnection of the electronic component 14 is provided among the solderballs constituting the BGA 24 as shown in FIG. 7B (the position of theconnection solder ball 24 a is not limited to that shown in the figure),that a hole reaching the heat conduction layer 17 is formed at theposition opposed to the connection solder ball 24 a, and that, when theelectronic component 14 is mounted, the connection solder ball 24 a ismelted and embedded inside the hole so as to make contact with the heatconduction layer 17. Furthermore, in the case that the electroniccomponent 14 is connected to the circuit board 13 by pins, it may alsobe possible that at least one connection pin 25 a not contributing tothe electrical connections of the electronic component 14 is providedamong the pins 25 as shown in FIG. 7C (the position of the connectionpin 25 a is not limited to that shown in the figure), that a holereaching the heat conduction layer 17 is formed at the position opposedto the connection pin 25 a, and that, when the electronic component 14is mounted, the connection pin 25 a is made so as to contact with theheat conduction layer 17.

The connection solder ball 24 a and the connection pin 25 a describedabove may be connected to the housing of the electronic component 14 ora member inside the electronic component 14 (for example, an individualcomponent, an internal circuit board or the like constituting theelectronic component 14). The generated heat can be transferred promptlyto the outside without being stored inside the electronic component 14by directly thermally contacting the connection solder ball 24 a or theconnection pin 25 a with the heating element inside the electroniccomponent 14. Hence, the temperature rise at the electronic component 14itself can be suppressed, and the performance of the electroniccomponent 14 can be improved.

Furthermore, although one heat conduction layer 17 is provided insidethe circuit board 13 in FIG. 3 to FIG. 6, the heat conduction layer 17according to the present invention should only be formed so that theheat conduction can be facilitated in the direction of the face of thecircuit board 13. For example, as shown in FIG. 8, multiple heatconduction layers 17 (two layers in the figure) may also be providedinside the circuit board 13. Moreover, it may also be possible to have aconfiguration wherein the multiple heat conduction layers 17 arethermally connected mutually by at least one connection portion 17 a ina way similar to that described above.

In addition, although the structure wherein the circuit board 13 isfixed by the protruding portion 11 a of the upper housing 11 and theprotruding portion 12 a of the lower housing 12 is provided in FIG. 3 toFIG. 6 and FIG. 8, it is also possible to provide a structure whereinthe heat transferred to the heat conduction layer 17 can be transferredpromptly to the upper housing 11 and the lower housing 12. For example,as shown in FIG. 9, it is also possible to have a structure wherein theportions of the heat conduction layer 17, corresponding to theprotruding portions 11 a and 12 a, are exposed partly or wholly so thatthe heat conduction layer 17 is thermally connected to at least part ofthe protruding portions 11 a and 12 a and so that the heat transferredto the heat conduction layer 17 is transferred promptly to the upperhousing 11 and the lower housing 12.

Furthermore, in the structures shown in FIG. 3 to FIG. 6 and FIG. 8 andFIG. 9, the heat conduction layer 17 may be formed on the whole face ofthe circuit board 13. However, the heat conduction layer 17 should onlybe structured so as to expand in the direction of the face of thecircuit board 13. Hence, the heat conduction layer 17 is not necessarilyrequired to be formed on the whole face of the circuit board 13, as longas the heat conduction layer 17 can promptly transfer the heat generatedin the electronic components 14 in the direction of the face of thecircuit board 13. For example, as shown in FIG. 10, the heat conductionlayer 17 may have a grid shape or a slit shape (the grids or slits mayhave regular shapes or irregular shapes being different in width orpitch).

Furthermore, in the case that the heat conduction layer 17 is formed ofa material having high electrical insulation, such as carbon, the heatconduction layer 17 is not short-circuited to the connection wires forconnecting the front and back faces of the circuit board 13. However, inthe case that the heat conduction layer 17 is formed of a metalmaterial, such as copper or aluminum, the heat conduction layer 17 is indanger of being short-circuited to the connection wires. In such a case,it is possible to form the heat conduction layer 17 on the whole face orpad of the circuit board 13 excluding the areas for the connection wires20, 21 as viewed in the normal direction of the circuit board 13 asshown in FIG. 11.

Furthermore, in the case that the heat conduction layer 17 is providedon the whole face of the circuit board 13, the heat generated in some ofthe electronic components 14 is also transferred to the other electroniccomponents 14, thereby raising the temperatures of the other electroniccomponents 14. The electronic components 14 are classified into twotypes: those hardly affected by temperature (heat-resistant components14 a that operate normally or have unvarying characteristics even whenthe temperature rises) and those easily affected by temperature(non-heat-resistant components 14 b that do not operate normally or havecharacteristics deteriorated when the temperature rises). In the casethat these two types of electronic components 14 are mixed together, itis undesirable that the temperatures of the non-heat-resistantcomponents 14 b are raised by the heat generated by some of theelectronic components 14. To solve this problem, it may be possiblethat, as shown in FIG. 12, the heat conduction layer 17 is formed on thewhole face or part of the circuit board 13 excluding the areas on whichnon-heat-resistant components 14 b are mounted, as viewed in the normaldirection of the circuit board 13, thereby to prevent the temperaturesin the vicinities of the non-heat-resistant components 14 b from rising.

The heat generated in the electronic components 14 can thus betransferred promptly in the direction of the face of the circuit board13 by arranging at least one heat conduction layer 17 having the shapeof a layer inside the circuit board 13 as described above. With thisconfiguration, it is possible to prevent the problem of the localtemperature rise at the keys 16 and the housing in the vicinities of theelectronic components 14 generating heat, and the heat can be radiatedefficiently to the outside. Furthermore, since the local temperaturerise can be suppressed, the degree of freedom in the selection of theelectronic components 14 increases, and it is possible to use electroniccomponents 14 having high performance. Still further, the rigidity ofthe circuit board 13 can be raised by forming the circuit board 13 tohave a multi-layer structure, whereby the reliability of the mobileterminal device 1 can be enhanced.

Next, a mobile terminal device and a heat radiating method according toa second embodiment of the present invention will be described referringto FIG. 14 and FIG. 15. FIG. 14 and FIG. 15 are sectional viewsschematically showing the structures of circuit boards inside the mobileterminal device according to the second embodiment. In this embodiment,although a mobile phone is also taken as an example of mobile terminaldevices and described below, such mobile terminal devices should only beequipped with at least an operation member and a display means.

The first embodiment described above is configured so that the heatgenerated in the electronic components 14 is transferred to the whole ofthe housing (the upper housing 11 and the lower housing 12) for holdingthe circuit board 13 on which the electronic components 14 are mounted,the key sheet 15 and the keys 16, whereby the heat is radiated. However,for the purpose of further raising heat radiation efficiency, it is alsopossible to have a configuration wherein the heat generated in theelectronic components 14 is transferred to the other componentsconstituting the mobile terminal device 1.

For example, the mobile terminal devices 1 of recent years are equippedwith a slot for accommodating a recording medium, such as a memory card.Even if the temperature of this slot rises to some extent, no problemoccurs in operation. Hence, for example, as shown in FIG. 14, in astructure wherein a second circuit board 13 a equipped with a slot 26 orthe like is fixed to the circuit board 13 according to the firstembodiment, at least one heat conduction layer 17 (the layer may be thesame as or different from the heat conduction layer 17 of the circuitboard 13) is also provided inside or on the surface of the secondcircuit board 13 a, and the heat conduction layer 17 of the circuitboard 13 is thermally connected to the heat conduction layer 17 of thesecond circuit board 13 a by a thermal connection member (a connectionportion 17 a also serving as a support rod for fixing the second circuitboard 13 a, a metal wire or the like).

With this structure, the heat generated in the electronic components 14is transferred from the heat conduction layer 17 inside the circuitboard 13 to the heat conduction layer 17 of the second circuit board 13a via the connection portion 17 a, the temperature of the slot 26 israised, and the heat thus is radiated, whereby heat-radiating paths canbe increased. As a result, it is possible to further suppress heattransfer to components that may cause problems when the temperaturerises, such as the keys 16.

In addition, the mobile terminal devices 1 of recent years mostly have afoldable structure to realize downsizing. In the case of a mobile-phone,as shown in FIG. 1, it is composed of two sections: a section whereinthe key operation section 2 is disposed, and a section wherein thedisplay section 3 is disposed. In this case, the temperature rise at thecomponents that the user touches directly, such as the keys 16, causeproblems. However, the sections that the user does not touch directly,such as the display section 3 and the housing for holding the displaysection 3, do not cause problems even if temperature rises to someextent. Hence, for example, as shown in FIG. 15, in a structure whereinthe circuit board 13 according to the first embodiment is connected to acircuit board 13 b on the display section side via a connection member,such as a flexible circuit board 13 c, at least one heat conductionlayer 17 (the layer may be the same as or different from the heatconduction layer 17 of the circuit board 13) is also provided inside thecircuit board 13 b on the display section side, and the circuit board 13is thermally connected to the circuit board 13 b on the display sectionside by a thermal connection member (the heat conduction layer 17, ametal wire or the like provided inside or on the surface of the flexiblecircuit board 13 c).

With this structure, the heat generated in the electronic components 14mounted on the circuit board 13 is transferred from the heat conductionlayer 17 inside the circuit board 13 to the heat conduction layer 17 ofthe circuit board 13 b on the display section side via the flexiblecircuit board 13 c. Hence, the temperatures of the housing for fixingthe circuit board 13 b on the display section side and other sectionsare raised, and the heat is radiated, whereby heat-radiating paths canbe increased. As a result, it is possible to further suppress heattransfer to components that may cause problems when the temperaturerises, such as the keys 16.

Although the heat conduction layer 17 is provided inside the circuitboard 13 according to each of the embodiments described above, thecircuit board 13 itself may be formed of a material having an excellentheat conductivity in which a heat conduction material is dispersed.Furthermore, although the mobile terminal device according to each ofthe embodiments described above is configured so that the keys 16 aredisposed on one face of the circuit board 13 via the key sheet 15 andthat the electronic components 14 are mounted on the other face, thedevice may also be configured so that these are disposed on the sameface of the circuit board 13.

1. A mobile terminal device comprising: a circuit board, heat-generatingcomponents disposed on one face of the circuit board, at least one firstheat conduction layer provided inside the circuit board, in which amember having a heat conductivity higher than that of the mainconstituent material of the circuit board is arranged in the directionof the face of the circuit board, an operation member on the face otherthan the face of the circuit board on which the heat-generatingcomponents are disposed, and at least one heat conduction suppressinglayer having a heat conductivity lower than that of the main constituentmaterial of the circuit board, said heat conduction suppressing layerbeing provided inside the circuit board and between the first heatconduction layer and the operation member, wherein the heat generated inthe heat-generating components is dispersed to the whole face of thecircuit board via the heat conduction layer.
 2. A mobile terminal deviceaccording to claim 1, wherein the mobile terminal device is a mobilephone.
 3. A mobile terminal device according to claim 1, wherein themobile terminal device is a mobile computer or a mobile game machine. 4.A heat radiating method for a mobile terminal device equipped with acircuit board on which heat-generating components are mounted, saidmethod providing, inside the circuit board, at least one first heatconduction layer in which a member having a heat conductivity higherthan that of the main constituent material of the circuit board isarranged in the direction of the face of the circuit board, therebydispersing the heat generated in the heat-generating components to thewhole face of the circuit board by the first heat conduction layer, andthe mobile terminal device further comprises an operation member, on theface other than the face of the circuit board on which theheat-generating components are mounted, wherein at least one heatconduction suppressing layer having a heat conductivity lower than thatof the main constituent material of the circuit board is provided insidethe circuit board and between the heat conduction layer and theoperation member, and the transfer of the heat generated in theheat-generating components to the operation member is suppressed by theheat conduction suppressing layer.